The FBI probe into the sex scandal that led to the resignation of CIA director David Petraeus has expanded to ensnare Gen. John R. Allen, the commander of U.S. and NATO troops in Afghanistan, the Pentagon announced early Tuesday. According to a senior U.S. defense official, the FBI has uncovered between 20,000 and 30,000 pages of "potentially inappropriate" e-mails between Allen and Jill Kelley, a 37-year-old Tampa woman whose close friendship with Petraeus ultimately led to his downfall. Allen, a Marine, succeeded Petraeus as the top allied commander in Afghanistan in July 2011.